//  https://en.wikipedia.org/wiki/Fibonacci_number

const fibonacci = ( N ) => {
    if ( N === 0 || N === 1 ) return N

  return fibonacci( N - 2 ) + fibonacci( N - 1 )
}

// testing
( () => {
  const number = 5
  console.log( number + 'th Fibonacci number is ' + fibonacci( number ) )
  } )()
